I have a kitchen with a shared neutral 20 amp circuit for 6 outlets. There is a 1000w microwave, refrigerator, toaster, and air frier. They will pop the breaker if we are not careful. Will creating 2 circuits help avoid trips? Also, could I go another way by wiring both circuits as standard 2 wire?
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I'm not sure of the distinction in your final question. How else would you create two circuits? I assume we're talking about a multi-wire branch circuit (two hots, one neutral on a dual breaker), right?– isherwoodCommented Feb 19 at 20:35
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4If you have two circuits with a shared neutral, and assuming that is installed properly as an MWBC and if your question is about adding in just another neutral so you still have the same two circuits but with two neutrals, again assuming it's done properly in the first place, that achieves nothing. Maybe you mean something else but your question is unclear.– jay613Commented Feb 19 at 21:49
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1Tip: If you are running the microwave and air fryer at the same time, they need their own circuits. I would add two 20A circuits to your kitchen.– John HanleyCommented Feb 20 at 18:36
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3 Answers
Breakers trip due to load on the hot, not the neutral. Splitting a MWBC into identical but isolated circuits doesn't change anything. You need to reduce load on each circuit, so you'd have to add a third circuit (or more).
If you have access, start by pulling a new home run for a dedicated microwave or fridge outlet, depending on which is easier. That alone may resolve your issue.
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Absolutely do this. You can control your use of the other appliances, and spread them across the two circuits according to usage or to who uses them. You can't control when the fridge comes on and you don't want it losing power. So this protects your most critical appliance and puts you in full control.– jay613Commented Feb 19 at 21:53
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Thanks for the answers. My panel was replaced recently by a licensed company. Just checked the breaker I mentioned and it is paired with another set of outlets on the other side of the kitchen so all is good there. Fridge idea might work. We have a run recently installed in the kitchen for something else and I will have to check on the fill of a conduit for viability to use. Commented Feb 19 at 22:28
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2Actually, I would create a dedicated circuit for the microwave, not the fridge. Most modern fridges pull 2-4 amps. A 1000w microwave is pulling 8.3 amps. Commented Feb 20 at 14:51
The key question is whether you have an overloaded Multi Wire Branch Circuit (MWBC) or a big dangerous mess.
A MWBC uses two hot wires on different legs with a shared neutral. This gives you 20A x 2 safely. If they are on the same leg but different breakers then it is unsafe because you could have 40A (if balanced between the breakers) on the neutral without a breaker trip, so that is not a valid MWBC but can start out as a valid MWBC that gets reconfigured incorrectly.
And there is a third scary possibility. Somebody takes the two hots of the MWBC and combines them on one breaker. That isn't so unsafe (because neutral can't get overloaded without hots getting overloaded and tripping the breaker) but can lead to nuisance trips (which may be what is happening in your situation).
Take a look at the breakers for this circuit:
- Two breakers on separate legs (240V between them) - proper MWBC and you are having actual overload and need to move some appliances or receptacles to another circuit
- Two breakers on same leg (0V between them) - bad MWBC and you need to move one hot/breaker to the other leg. Since it is a MWBC must be breakers next to each other, double breaker or handle tied
- one breaker with two hot wires - split to a proper two breaker MWBC.
If you have a proper MWBC then the problems are likely the combination of:
- Microwave
- Toaster
- Air Fryer
Each of those could easily use 1000W or more, and 2,400W is the limit on a 20A circuit. If they are all 3 on the same hot then that is a guaranteed problem and rearranging things will help. MWBCs can be wired a bunch of different ways. One common way is one hot on the top receptacle and the other hot on the bottom receptacle of several duplex receptacles. If that's the case then it should be easy to rearrange things. However, an MWBC can also come in to a box and split at (or even before) the first receptacle, so it can be hard to figure out what's what without taking off cover plates to check the wiring.
answered Feb 19 at 20:48
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I wish there was a commonplace form of receptacle with a built-in 20A breaker that could be installed on a 40A or 50A circuit, since a fair number of appliances draw around 12-13 amps. Three such devices could be used on a 40A circuit, but trying to put two on either of the 20A circuits in a typical kitchen would often result in a popped breaker.– supercatCommented Feb 20 at 17:40
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There are plenty of reasons why that would not be a good idea. But that is the reason why you sometimes find a subpanel in/near a kitchen. (I am fortunate that my kitchen is directly above the laundry room where the electrical panel is, so running extra circuits to the kitchen is super-easy. Most people aren't that fortunate.) Commented Feb 20 at 17:50
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2Why would having a breaker next to the receptacle it controls be a bad idea? If a breaker was designed to be water-resistant, what downside would you see?– supercatCommented Feb 20 at 18:33
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1Thanks for noting that shared-neutral circuits are often a big dangerous mess. They can start safe and then homeowners move stuff around not understanding the consequences and end up with 40 amps on the neutral. That was the case in my house when I bought it and in several older houses owned by friends that I've helped diagnose electrical problems. It is surprisingly common. Commented Feb 20 at 19:10
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1@EricLippert Found a miswired (both hots on same leg) MWBC in an old fusebox when replacing two fuseboxes + 1 small breaker panel (added when doing my kitchen 20+ years ago) with 1 nice big breaker panel. Fortunately it never caused a problem, but it could have. Commented Feb 20 at 20:48
The refrigerator is a negligible load. Yes I know it's 5 times larger than a microwave oven and therefore "should" take 5 times the power LOL, but no, refrigerators cheat because they are heat pumps. It may blow 600 watts worth of heat out its back and sides, but it only take it about 100 watts to do that. It's not making that heat, it's moving it from inside the fridge. So the refrigerator is a non-factor in your breakers tripping.
However in a shared-neutral or MWBC circuit, you have 2 hot wires, one per pole of supply power, which independently have 20 amps of capacity each. A typical heat-making kitchen appliance with a normal 15A plug draws 12 amps because of NEC 210.21. Except 2-slice toasters are special, they are 6 amps so they can simply put two of them in a double-toaster (4-slice toaster). If you only use one side of a double toaster, it's 6 amps.
So your problem is that you are incorrectly stacking loads on the two MWBC half-circuits. You are stacking the air fryer with the microwave on the same half-circuit (pole), busting 20A and getting a breaker trip. Or possibly even all 3 appliances on the same pole.
You need to figure out which sockets are on which pole, and distribute your loads evenly so neither pole exceeds 20A.
If you have an extension cord and are handy and safe with a voltmeter, the easy way to do this is measure the voltage between hot pins (the shorter pin) on 2 different sockets. Danger: 240V! If the voltmeter measures 0 volts, they are on the same pole. If it measures 240V or 208V, they are on opposite poles. Then you can label them 1 and 2, red and black, or whatever makes you happy.
Note that on any given receptacle, the two sockets CAN be on opposite poles.
answered Feb 20 at 22:56
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